diff --git a/components/bugzilla.py b/components/bugzilla.py
index 4cabd95..794599f 100644
--- a/components/bugzilla.py
+++ b/components/bugzilla.py
@@ -11,7 +11,7 @@
 class CommentTemplates:
     @staticmethod
     def UPDATE_SUMMARY(library, new_release_version, release_timestamp):
-        return "Update %s to new version %s from %s" % (
+        return "Update %s to new version %s from %s UTC" % (
             library.name, new_release_version, release_timestamp)
 
     @staticmethod
diff --git a/components/utilities.py b/components/utilities.py
index 860ee9d..39536a8 100644
--- a/components/utilities.py
+++ b/components/utilities.py
@@ -11,6 +11,7 @@
 import functools
 import time
 
+from datetime import timezone
 from dateutil.parser import parse
 
 RETRY_TIMES_OVERRIDE = None
@@ -66,7 +67,13 @@ def raise_(e):
 
 
 def string_date_to_uniform_string_date(s):
-    return parse(s).strftime('%Y-%m-%d %H:%M:%S')
+    # Hosts report commit times with an offset (gitlab: "...+10:00"), as UTC
+    # ("...Z"), or with no zone at all (googlesource, which is UTC). Normalize
+    # them all to UTC so the result doesn't depend on the committer's timezone.
+    d = parse(s)
+    if d.tzinfo is not None:
+        d = d.astimezone(timezone.utc)
+    return d.strftime('%Y-%m-%d %H:%M:%S')
 
 
 def merge_dictionaries(a, b, ignored_dicts=[], ignored_keys=[]):
diff --git a/tests/bugzilla.py b/tests/bugzilla.py
index d4f74f0..ab5387e 100755
--- a/tests/bugzilla.py
+++ b/tests/bugzilla.py
@@ -43,7 +43,7 @@ def do_POST(self):
                 'product': 'Core',
                 'component': 'ImageLib',
                 'type': "enhancement",
-                'summary': 'Update dav1d to new version V1 from 2020-08-21 15:13:49',
+                'summary': 'Update dav1d to new version V1 from 2020-08-21 13:13:49 UTC',
                 'description': '',
                 'whiteboard': '[3pl-filed]' + task_id_whiteboard(),
                 'cc': ['tom@mozilla.com', 'jewilde@mozilla.com', 'additional@example.com'],
diff --git a/tests/mach_vendor.py b/tests/mach_vendor.py
index 3c01423..99da347 100644
--- a/tests/mach_vendor.py
+++ b/tests/mach_vendor.py
@@ -45,6 +45,18 @@ def testISO8601Timestamp(self):
             self._check_for_update(REVISION + " 2026-09-09T17:56:48Z"),
             (REVISION, "2026-09-09 17:56:48"))
 
+    def testOffsetTimestampIsConvertedToUTC(self):
+        # gitlab and codeberg report the committer's local time with an offset;
+        # the uniform date must be UTC, not the committer's wall-clock time.
+        self.assertEqual(
+            self._check_for_update(REVISION + " 2026-09-25T12:59:00.000+10:00"),
+            (REVISION, "2026-09-25 02:59:00"))
+
+    def testNegativeOffsetCrossesMidnight(self):
+        self.assertEqual(
+            self._check_for_update(REVISION + " 2026-09-17T22:36:18.000-04:00"),
+            (REVISION, "2026-09-18 02:36:18"))
+
     def testNoUpdateAvailable(self):
         self.assertEqual(self._check_for_update(""), (None, None))